There appears to be a healthy competition developing between optical and electrical communication systems. If electrical systems are to remain viable for distributing signals at high transmission speeds, then electrical cables and connectors must improve their transmission performance or face replacement by optical systems. However, since nearly all consumer and business communication systems are equipped to handle electrical signals exclusively, electrical systems presently enjoy a competitive advantage. Nevertheless, the replacement of electrical equipment with optical equipment may ultimately occur anyway, but it can be forestalled for the foreseeable future by substantial improvements in high-frequency performance.
In an electrical communication system, it is sometimes advantageous to transmit information (video, audio, data) in the form of balanced signals over a pair of wires (hereinafter "wire-pair") rather than a single wire, wherein the transmitted signal comprises the voltage difference between the wires without regard to the absolute voltages present. Each wire in a wire-pair is capable of picking up electrical noise from sources such as lightning, automobile spark plugs and radio stations to name but a few. Balance is a measure of impedance symmetry in a wire pair as between its individual conductors and ground. When the impedance to ground for one conductor is different than the impedance to ground for the other conductor, then common mode (longitudinal) signals are undesirably converted to differential mode (transverse) signals. Additionally, return loss comprises a reflection of the incoming signal that effectively occurs when the terminating impedance does not match the source impedance. Of greater concern, however, is the electrical noise that is picked up from nearby wires that may extend in the same general direction for long distances. This is referred to as crosstalk, and so long as the same noise signal is added to each wire in the wire-pair, then the voltage difference between the wires will remain about the same. In all of the above situations, undesirable signals are present on the electrical conductors that can interfere with the information signal.
An example of an electrical communication system where crosstalk is likely to occur is shown in FIG. 1, which discloses a high-speed communication terminal 1 and cables 2, 3--each containing several wire-pairs. Electrical interconnection between cables may be facilitated by the use of standard telecommunications connectors that are frequently referred to as modular plugs and jacks, or other style plugs and receptacles. Connecting apparatus includes a modular plug 20, and a modular jack 30 that comprises a jack frame 310 and a connector assembly 320. Modular plug 20 inserts into opening 315 on the front side of jack frame 310 and communicates electrical signals to and from terminal 1. Inserted into the back side of jack frame 310 is a connector assembly 320, which receives and holds wires from cable 3 that are individually pressed into slots 321 where mechanical and electrical connection is made. And while there are many places in FIG. 1 where undesirable signals attributable to crosstalk, imbalance and return loss are present, it is particularly desirable to reduce the undesirable signals that arise within connecting apparatus 20, 30.
Connecting apparatus 20, 30 may include up to eight or more wires that are close together--a condition that leads to excessive crosstalk over relatively short distances. If the electrical conductors that interconnect with these terminals are close together for any distance, as is the case in present designs, then crosstalk between these wire-paths is particularly troublesome. In particular, near-end crosstalk (NEXT), which is the crosstalk energy traveling in the opposite direction to that of the signal in the disturbing wire-pair, is about 25 dB below the level of the incoming signal at 100 MHz in modular jack designs such as shown in U.S. Pat. No. 5,096,442 that issued on Mar. 17, 1992. One such modular jack is known as the M1 Communication Outlet, which is manufactured by Lucent Technologies. FIG. 2 illustrates the polarity and magnitude of the NEXT between two pairs of conductors within the plug 20 and jack 30 by positive (+) signs. Note that the overall NEXT in the connecting apparatus comes from both the plug 20 and jack 30. Because the conductor paths within the plug and jack are close together and extend in a straight line, NEXT is substantial.
U.S. Pat. No. 5,186,647 (the '647 patent) issued on Feb. 16, 1993 and made a substantial improvement to the design of modular jacks by crossing the path of one of the conductors within the connector, over the path of another of the conductors within the connector. This was the first time that compensating crosstalk was added to the undesirable crosstalk within an electrical connector in an attempt to cancel it. FIG. 3 illustrates the polarity and magnitude of the NEXT between two pairs of conductors within the plug 20 and jack 30 by positive (+) and negative (-) signs. This simple technique improves NEXT at 100 MHz, by a startling 17 dB, thereby enabling the electrical connector to comply with the Category 5 requirements specified in ANSI/EIA/TIA--568A. An example of such a modular jack is the M100 Communication Outlet, which is manufactured by Lucent Technologies. In FIG. 3, offending crosstalk is shown in Section 0 coming from the plug 20 and a first portion of jack 30; while compensating crosstalk is shown in Section I coming from a second portion of jack 30.
Techniques have been developed for further reducing crosstalk in the present generation of electrical connectors, where levels that are about 46 dB below the level of the incoming signal at 100 MHz have been achieved. An example of such a connector is the MPS100 Communication Outlet, which is also manufactured by Lucent Technologies. Nevertheless, what is desired, but is not disclosed in the prior art, is a technique for improving the balance and return loss characteristics of an electrical connector and, more particularly, a technique for reducing crosstalk in the electrical connector to levels that are more than 46 dB below the level of the incoming signal at 100 MHz